The present invention relates to a connected body comprising a gas separator and a metal and to an apparatus for separating hydrogen gas selectively and effectively from a mixed gas to be treated.
Hydrogen gas is used in a great amount in the field of petrochemistry and is highly expected as a clean energy source. A natural gas, naphtha, or the like is first converted, by a catalyst, to a hydrogen-containing gas, from which hydrogen gas is then separated to give a hydrogen gas with high purity.
Only hydrogen gas dissolves in palladium and palladium alloy, thereby hydrogen gas can be selectively separated from a mixed gas. Japanese Patent Application Laid-Open 273030/1987 and Japanese Patent Application Laid-Open 171617/1988 each disclose a gas separator which is produced by covering the surface of a porous substrate with a gas separation membrane consisting of palladium or a palladium alloy. The porous substrate is made of porous glass or a ceramic such as aluminum oxide. Since a palladium membrane itself does not possess sufficient mechanical strength, the palladium membrane is coated onto a substrate. Hydrogen gas is effectively separated from a mixed gas, using a gas separation membrane, by accelerating a speed of the gas diffusion in the gas separation membrane. Therefore, hydrogen gas is preferably separated from a mixed gas under a high pressure in the range of 5-10 atm. at a high temperature of 300.degree. C. or higher, more preferably 500.degree. C. or higher. In this step, the important points are airtightness and durability of joints between the gas separator and its supporters. That is, the joints are required to have durability and no leakage of the mixed gas or the separated gas.
An apparatus for separating hydrogen gas from a mixed gas has a structure that a gas containing hydrogen gas is introduced from one side of the gas separator and that only hydrogen gas can penetrate the gas separator so as to give refined hydrogen gas from the other side of the gas separator. Therefore, a mixed gas to be treated on one side has to be airtightly separated from the refined hydrogen gas on the other side in the apparatus, and it is important that a gas to be treated does not leak out to the side for the refined hydrogen gas from the joints between the gas separators and the supporters.
There is a conventional apparatus for separating hydrogen gas from a mixed gas. In the apparatus, a gas separator is connected with the supporters by means of O-rings. However, the apparatus can be used only at 200.degree. C. or lower, and it is not easy for the apparatus to maintain the airtightness at a temperature higher than 200.degree. C. A joint which can be used at 500.degree. C. or higher has not been developed.
When a gas separation membrane is formed by chemical metal-plating on the surface of a gas separator and of a joint where the gas separator is connected with the supporter by means of a glass, the glass does not adhere sufficiently to the gas separation membrane. The gas separation membrane sometimes exfoliates from the joint where a glass is used, causing the leakage of a mixed gas into a refined gas.
A gas separator has a tubular ceramic substrate and a gas separation membrane on the outer surface of the substrate. A metallic supporter has at least one hole through which or into which the gas separator is inserted. When a gas separator is connected with a metallic supporter by means of wax, the gap between the surface of the gas separation membrane and the hole of the supporter is required to be 100 .mu.m or less. However, it is difficult to produce a tubular gas separator having such a precise and accurate diameter.
Hence, the present invention aims to provide a connected body having a gas separator and a metal and an apparatus for separating hydrogen gas from a mixed gas. In the connected body, the joint between a gas separator and a metal is airtight and the mixed gas does not leak in the refined hydrogen gas even if the hydrogen gas is separated from the mixed gas at 200.degree. C. or higher.